// @algorithm @lc id=100345 lang=cpp
// @title qiu-12n-lcof

#include "algm/algm.h"
#include <iostream>
#include <string>
#include <vector>
using namespace std;
class Solution {
public:
    int sumNums(int n) {
        n && (n += sumNums(n - 1));
        return n;
    }
};